The present invention relates to a process and apparatus for manufacturing articles such as pipe insulation tubes from a foamed material and more particularly involves process and apparatus for manufacturing a highly flexible, impermeable article from a foamed polymer such as polyethylene or polypropylene.
The prior art teaches methods of foaming polymers such as polystyrene as well as the foaming of elastomers such as synthetic rubbers. It is known that products manufactured from foamed polymers and elastomers exhibit good insulation properties under certain circumstances. For example, foamed polystyrene when foamed in large flat sheets has been used for insulation in home building between outer and inner wall structures. Likewise, foamed elastomers such as rubber have been used for insulation of air conditioning and water pipes in home and commerical construction. It is known that other polymers such as polyethylene can be foamed to provide advantageous insulating material. Unfortunately, all of the known polymers and elastomers suffer disadvantages when utilized as insulating material.
For example, when polymers such as polystyrene and polyethylene are foamed to form insulation, the resulting product is generally very stiff and/or brittle and therefore difficult to utilize on objects such as water pipes and air conditioning tubing which have considerable numbers of bends and curves. On the other hand, a foamed synthetic rubber such as neoprene provides a flexible insulating material, but one that is very expensive in cost due to the raw material cost. Also, many if not all of the elastomers utilized as foamed insulation suffer from being permeable to moisture which, as a result cuts down the insulating properties of the material and also allows migration of moisture into the insulated line thereby allowing corrosion and mildew to form.
In addition to these disadvantages, many pure elastomers which are foamed to form insulation do not provide a flexible final product because of cross-linking in the elastomer. In addition foamed rubbers are subject to degradation by the ozone content of the atmosphere and by ultra violet rays from natural sunlight and other sources. Furthermore the finished foamed product made of pure elastomers has a final bulk density of approximately six pounds per cubic foot. On the other hand, foamed polyethylene has a bulk density of just two pounds per cubic foot. Thus, even if the material costs were equal between elastomer and polymer, three times as much elastomer is required per unit volume than polymer thus making the relative cost of foamed elastomer at least three times that of the foamed polymers. Also, the manufacture of insulation utilizing foamed elastomer requires the use of an expensive heating system such as a radio-wave oven to heat the elastomer to form the necessary cross-linking.
The present invention overcomes these disadvantages of the prior art by providing a process for manufacturing foamed materials which exhibit high flexibility and high impermeability. These materials are formed from a blend of a polymer such as polyethylene with an elastomer such as polyisobutylene.